Cleaning composition containing tetraalkylammonium salt and use thereof in semiconductor fabrication

ABSTRACT

A composition prepared from water, hydrofluoric acid (HF) and tetraalkylammonium hydroxide (TAAH, preferably tetramethylammonium hydroxide (TMAH)) or tetraalkylammonium fluoride and solvent with or without HF or TAAH is used to clean residue from a semiconductor wafer, where the residue is formed as a result of a planarization process, such as chemical mechanical polishing. Incorporation of TMAH into an aqueous HF composition retards the rate at which the composition dissolves borophosphosilicate (BPSG) without effecting the rate at which silica is dissolved. Thus, the aqueous HF/TMAH composition may be used to completely remove silica-containing residue from a BPSG surface, with a tolerable level of BPSG removal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/097,557, now U.S. Pat. No. 6,044,851, filed Jun. 15, 1998, which is acontinuation of application Ser. No. 08/725,579, filed Oct. 3, 1996,issued as U.S. Pat. No. 5,855,811.

TECHNICAL FIELD

The present invention relates to semiconductor fabrication, and moreparticularly to removing residue from a semiconductor wafer that hasbeen subjected to planarization.

BACKGROUND OF THE INVENTION

The present-day fabrication of semiconductor wafers is a complexmulti-step process. In a typical process, various materials aresequentially applied to a substrate in order to build up a substantiallylaminar structure. After a layer has been laid down, selected regions ofthat layer are commonly modified or removed. Such manipulations oftenimpart nonplanarity to the top surface of the layer. Nonplanarity, alsoknown as uneven surface topography, is undesirable for a number ofreasons, one of which is that laying down a subsequent layer is mademore difficult if the underlying layer is nonplanar. Therefore, a commonstep during semiconductor wafer fabrication is to planarize the surfaceof the wafer, by a process known as planarization or polishing, wherethese terms are often used interchangeably.

There are a large number of specific processes that can be used toplanarize the surface of a semiconductor wafer, a few of which will bediscussed later herein. However, it is generally the case thatplanarization will selectively remove surface material that constitutesthe highest points of the surface, i.e., the points of the surfacefurthest from the base of the semiconductor wafer. In this way, the highpoints are removed and the surface topography of the wafer isplanarized, also called leveled or flattened. The planarization processcan be carried out on an already planar surface, in which case an entirelayer of a semiconductor wafer may be removed. Regardless of the amountof material that is removed by a planarization process, a typicalconsequence of planarization is that a residue is left on the planarizedsurface. This residue may be termed planarization residue.

The exact identity of the residue depends on the details of theplanarization process, however at a minimum the residue typicallyincludes bits and particles which have been dislodged from the surface,and often includes materials that were used to assist the planarizationprocess. At the end of the planarization process, this residue should becompletely removed before any further layers may be laid down upon thesemiconductor surface.

Pure water, optionally in combination with scrubbing, is commonly usedin the art to remove planarization residue. However, the prior art alsodescribes methods and compositions which have been developed to moreeffectively and efficiently remove planarization residue from asemiconductor surface. For example, U.S. Pat. No. 5,478,436 toWinebarger et al. is directed to applying a cleaning solution to asemiconductor substrate having metal contaminants thereon, in order toremove the metal contaminants. The Winebarger et al. cleaning solutioncomprises an organic solvent and a compound containing fluorine. Asanother example, U.S. Pat. No. 5,389,194 to Rostoker et al. is directedto a method of cleaning polishing residue from a semiconductor device.The Rostoker et al. method uses a cleaning solution consistingessentially of phosphoric acid and hydrofluoric acid.

As recognized by both Winebarger et al. and Rostoker et al., a problemwith the use of chemical-containing cleaning solutions for removingplanarization residue is that, in order for the cleaning process to beeffective, the cleaning solutions are so strong that theydegrade/dissolve the surface layer itself. That is, the cleaningsolutions cause undesirable degradation and/or removal of the surface ofthe planarized layer. While Winebarger et al. and Rostoker et al. bothpurport to address this problem, there is still a significant need inthe art for satisfactory processes and cleaning solutions forselectively removing planarization residue from a semiconductor surface.

SUMMARY OF THE INVENTION

The present invention provides a process for effectively removingplanarization residue from a planarized surface, with acceptable affectson the planarized surface itself. The process comprises the steps ofproviding a semiconductor wafer surface having residue thereon, wherethe residue is a consequence of a planarization process, and thencontacting the residue with a cleaning composition to remove at leastsome of the residue from the surface. In a preferred embodiment of theinvention, the cleaning composition is a solution comprisingtetraalkylammonium fluoride (TAAF) of the formula (R)₄NF wherein eachoccurrence of R is independently a C₁₋₂₂alkyl group. In anotherpreferred embodiment of the invention, the composition results from thecombination of solvent, hydrofluoric acid (BF) and tetraalkylammoniumhydroxide (TAAH), where TAAH has the formula (R)₄NOH and each occurrenceof R is independently a C₁₋₂₂alkyl group.

Another aspect of the invention is a process for fabricating asemiconductor device. The process includes the steps of providing asemiconductor device having a surface, and then planarizing the surfaceto provide a planarized surface having residue thereon. The residue iscontacted with a cleaning composition as described above. In this way, asemiconductor device may be planarized, and then residue from theplanarization process may be subsequently removed.

A related aspect of the invention is a semiconductor device that hasbeen prepared by the above-described process.

A further related aspect of the invention is a preferred process forpreparing a cleaning composition useful in the above-processes. Thepreferred process includes the steps of adding hydrofluoric acid (HF) towater to form dilute HF, and then adding TAAH to the dilute HF. In apreferred embodiment of the invention, 0.01 to 100 volume parts of 0.1to 50 wt % aqueous HF are added to 100 volume parts of water to formdilute HF, and then 0.01 to 100 volume parts of 0.1 to 25 wt % aqueousTAAH are added to the dilute HF. More preferably, 0.1 to 10 volume partsof 10 to 50 wt % aqueous HF are added to 100 volume parts of water toform dilute HF, and then 0.1 to 10 volume parts of 5 to 25 wt % aqueousTAAH are added to the dilute HF. Preferably, the TAAH istetramethylammonium hydroxide. In a preferred embodiment, at least oneorganic solvent and/or at least one surfactant is additionally added tothe cleaning composition.

The invention is also directed to a preferred composition that may beused to clean residue from a surface previously subjected toplanarization. According to one aspect of the invention, the compositionresults from the combination of water, hydrofluoric acid (HF),tetraalkylammonium hydroxide and at least one of organic solvent andsurfactant. According to another aspect of the invention, thecomposition results from combining tetraalkylammonium fluoride and atleast one of water, organic solvent and surfactant. In a preferredembodiment, the cleaning composition results from the combination ofwater, 0.1-49 wt % aqueous HF and 0.1-25 wt % (aqueous or non-aqueous)TAAH in a water:HF solution:TAAH solution volume parts ratio of100:0.0.1-100:0.01-100. More preferably, the volume parts ratio is100:0.1-10:01.-10, and still more preferably the volume parts ratio is100:0.5-2:0.5-5. One preferred cleaning composition has an alkaline pH,for example, a pH of about 9 to about 13, and preferably about 11.Another preferred cleaning composition has an acidic pH, for example, apH of about 1 to about 5, preferably about 3.5. The group “R” in theTAAH or TAAF is preferably independently C₁₋₄alkyl at each occurrence,where the TAAH is preferably tetramethylammonium hydroxide. A surfactantis preferably present in the composition at a concentration of about0.001 to about 5.0 wt %, more preferably about 0.01 to 1 wt % based onthe total weight of cleaning composition, where preferred surfactantsare nonionic, and suitable surfactants are TRITON-X (Rohm and Haas Co.,Philadelphia, Pa.) and ACATIONOX (Baxter-Scientific, McGaw Park, Ill.).An organic solvent may be present in a preferred composition, where theorganic solvent is preferably present at a concentration of about 0.01to about 95 wt % based on the total weight of the composition. In apreferred embodiment, the organic solvent contains hydroxylfunctionality. Suitable organic solvents include methanol, ethanol,n-propanol, iso-propanol, ethylene glycol and propylene glycol.

These and other aspects of this invention will become apparent uponreference to the following detailed description and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is graphical representation of the effect on pH of titrating TMAHinto aqueous HF of various concentrations.

FIG. 2 is a flow diagram illustrating a process for fabricating asemiconductor device in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a composition that is useful in removingresidue from the surface of a semiconductor wafer that has beensubjected to planarization. In a preferred embodiment of the invention,the composition comprises a solution of tetraalkylammonium fluoride(TAAF). In another preferred embodiment of the invention, thecomposition results from combining at least the following threechemicals: solvent, and preferably water (H₂O and/or isotopes thereof,hereinafter simply “water”), hydrogen fluoride (HF and/or isotopesthereof, hereinafter simply “HF”) and tetraalkylammonium hydroxide (TAAHand/or isotopes thereof, herein after simply “TAAH”). This latercleaning composition, when it contains water, may be referred to hereinas aqueous HF/TAAH or, more simply, as aq. HF/TAAH.

The phrase “the composition results from combining” solvent, HF and TAAHas used herein is meant to refer to the composition itself, regardlessof how that composition is prepared and regardless of what thatcomposition contains. Thus, the cleaning composition used in theinvention may be prepared by means other than combining solvent, HF andTAAH, and still afford the composition of the present invention as longas the same composition could have been formed by combining solvent, HFand TAAH. Preferably, the cleaning composition is prepared by combiningwater, HF and TAAH.

Furthermore, it is not necessarily the case that the composition whichresults from a combination of solvent, HF and TAAH contains each ofsolvent, HF and TAAH. It may or may not happen that two or more of theseingredients react together upon combination and form a reaction productwhich has a chemical structure unlike the starting materials. Because HFis an acid and TAAH is a base, there may be some ion exchange that takesplace when these materials are combined, such that tetraalkylammoniumfluoride (TAAF) and water is formed. However, the cleaning compositionsof the present invention encompass compositions that are the result ofsuch chemical reaction and/or ion exchange.

The TAAF has the formula (R)₄NF, and can be described as the fluoridesalt of a tetraalkylammonium ion. Each alkyl group, R, of the ammoniumion has at least one and may have as many as about 22 carbon atoms,i.e., is a C₁₋₂₂alkyl group. The carbon atoms of each R group may bearranged in a straight chain, a branched chain, a cyclic arrangement,and any combination thereof. Each of the four R groups of TAAF areindependently selected, and thus there need not be the same arrangementor number of carbon atoms at each occurrence of R in TAAF. For example,one of the R groups may have 22 carbon atoms, while the remaining threeR groups each have one carbon atom. Tetramethylammonium fluoride (TMAF)is a preferred TAAF. Tetraethylammonium fluoride (TEAF) is anotherpreferred TAAF. A preferred class of TAAF has alkyl groups with one toabout four carbon atoms, i.e., R is a C₁₋₄alkyl group, while anotherpreferred class of TAAF has alkyl groups with two to about four carbonatoms, i.e., R is a C₂₋₄alkyl group. The TAAF may be a mixture, e.g., amixture of TMAF and TEAF.

Tetramethylammonium fluoride is available commercially as thetetrahydrate, with a melting point of 39-42° C. Aldrich Chemical Co.,Milwaukee, Wis., sells this tetramethylammonium fluoride. The hydrate oftetraethylammonium fluoride is also available from the Aldrich ChemicalCo. Either of these materials, which are exemplary only, may be used inthe practice of the present invention. Tetraalkylammonium fluorideswhich are not commercially available may be prepared in a manneranalogous to the published synthetic methods used to prepare TMAF andTEAF, which are known to one of ordinary skill in the art.

To prepare a cleaning composition from TAAF, the TAAF is combined with asolvent. The solvent may be water, an organic solvent, or a combinationthereof Suitable organic solvents include hydroxyl-containing solventssuch as methanol, ethanol, n-propanol, iso-propanol, n-butanol,t-butanol, iso-butanol, sec-butanol, ethylene glycol, propylene glycoland mono- and polyhydric alcohols having higher carbon number. Thecomposition is easily prepared simply by combining TAAF and solvent, andmixing these materials together to form a homogeneous composition,preferably a solution.

The solvent from which the cleaning composition may be prepared ispreferably a pure water, in other words, is preferably water that iscompletely or substantially free of organic and inorganic material.Impurities are undesirable for several reasons, a primary reason beingthat the impurities may find their way onto the semiconductor devicebeing cleaned of residue, and thus hinder the formation of a cleansurface. Some spring waters are naturally pure, and are suited for usein the present invention. Otherwise, impure water may be brought to thepure state preferred for the invention by one or more of a number oftechniques known in the water-purification art, including distillation(which provides “distilled water”) and/or passing the water through anion exchange resin (which provides “deionized water”). In fact,distilled water is essentially free of metal ions, and so may also bereferred to as a deionized water. The water may be repeatedly passedthrough distillation columns and/or ion exchange resins to increase thepurity of the water. Distillation equipment and ion exchange resins arecommercially available from a number of sources, as listed in, forexample, The Thomas Directory. Purified water is available from, e.g.,Aldrich Chemical Co., Milwaukee, Wis. among many other suppliers.

However, any liquid material which dissolves the ET, TAAH and/or TAAFmay be employed as the solvent. Alcohols are a preferred class ofsolvent, where lower molecular weight alkanols such as C₁₋₄ monohydricor dihydric alcohols are preferred.

HF, which is a gas, will cause serious harm when contacted with humanskin, and thus should be a handled very carefully. It is availablecommercially as a solution in water, and it is preferably obtained andworked with in that form (albeit still very carefully, as aqueous HF isalso hazardous to human skin). Aldrich Chemical Co., among many othersuppliers, sells aqueous HF at various HF concentrations. Essentiallyany concentration of HF in water may be employed in preparing theinventive compositions, for example, compositions having from about 0.1wt % to about 50 wt % HF in water are suitable. An aqueous HF containingessentially 49 wt % HF and 51 wt % water is a standard material ofcommerce, and is a preferred material for use in the present invention.If a non-aqueous cleaning composition is desired, then HF gas may bebubbled into an organic solvent, such as methanol, to which may also beadded TAAF or TAAH.

The TAAH has the formula (R)₄NOH, and can be described as the hydroxidesalt of a tetraalkylammonium ion. Each alkyl group, R, of the ammoniumion has at least one and may have as many as about 22 carbon atoms,i.e., is a C₁₋₂₂alkyl group. The carbon atoms of each R group may bearranged in a straight chain, a branched chain, a cyclic arrangement,and any combination thereof. Each of the four R groups of TAAH areindependently selected, and thus need not have the same arrangement ornumber of carbon atoms at each occurrence. For example, one of the Rgroups may have 22 carbon atoms, while the remaining three R groups eachhave one carbon atom. Tetramethylammonium hydroxide (TMAH) is apreferred TAAH. Tetraethylammonium hydroxide (TEAH) is another preferredTAAH. A preferred class of TAAH has alkyl groups with one to about fourcarbon atoms, i.e., R is a C₁₋₄alkyl group, while another preferredclass of TAAH has alkyl groups with two to about four carbon atoms,i.e., R is a C₂₋₄alkyl group. The TAAH may be a mixture, e.g., a mixtureof TMAH and TEAH.

TMAH is commercially available as the pentahydrate (a solid, with amelting point of 65-68° C.) at a purity of 99% from Aldrich Chemical Co.Solutions of TMAH are also commercially available. For example, AldrichChemical Co. sells 10 wt % and 25 wt % TMAH in water, and 25 wt % TMAHin methanol. TMAH from any of these sources is suitably employed inpreparing the cleaning composition of the invention. Othertetraalkylammonium hydroxides are also commercially available. Forexample, tetraethylammonium hydroxide (TEAH), tetrapropylammoniumhydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH) are availablefrom Aldrich Chemical Co. Tetraalkylammonium hydroxides which are notcommercially available may be prepared in a manner analogous to thepublished synthetic methods used to prepare TMAH, TEAH, TPAH and TBAH,which are known to one ordinary of skill in the art. TAAH may bedissolved in water at essentially any concentration, and be suitable foruse in preparing the cleaning composition. For example, a TAAHconcentration of about 0.1 wt % to about 25 wt % in solvent (preferablywater) is suitable.

Each of the solvent, TAAF, HF and TAAH is preferably of electronic gradepurity or better.

As stated above, the cleaning composition may be prepared from solvent,HF and TAAH or from TAAF and a solvent. The composition may additionallybe prepared from optional components. A preferred optional component isa surfactant. The surfactant may be nonionic, cationic or anionic.TRITON-X (Rohm and Haas, Philadelphia, Pa.) and ACATIONOX(Baxter-Scientific, McGaw Park, Ill.) are preferred,commercially-available non-ionic surfactants.

Where water is the solvent, another preferred optional component is oneor more organic solvents. Low molecular weight solvents containing oneor more hydroxyl groups are a preferred class of organic solvent.Exemplary hydroxyl-containing solvents include, without limitation,methanol, ethanol, n-propanol, iso-propanol, n-butanol, t-butanol,iso-butanol, sec-butanol, propylene glycol and ethylene glycol. Theorganic solvent may be present in an amount ranging from about 0.01 wt %to about 95 wt %, so that the cleaning composition may be completelyaqueous, or may be essentially organic with water present as only aminor ingredient.

Still other optional ingredients include, without limitation, aceticacid, citric acid, phosphoric acid, ammonia and other common processchemicals.

The precise amounts of solvent, TAAF, HF and TAAH used to form thecleaning composition can each vary over a very wide range. As expressedin volume parts (a general term to represent, e.g., gallons, liters,etc.) and using water as an exemplary solvent, to every 100 volume partsof water used to form the composition, between about 0.01 to 100 volumeparts 49 wt % HF and between about 0.01 to 100 volume parts 25 wt % TAAHmay be used. Expressed in a volume parts ratio, this is equivalent to100:0.01-100:0.01-100. Stated in the same terms (water:49 wt % HF:25 wt% TAAH), a preferred volume parts ratio is 100:0.1-10:0.1-10, and a morepreferred volume parts ratio is 100:0.5-2:0.5-5.

The relative amounts of HF and TAAH used in forming the cleaningcomposition will be reflected in the final pH of the composition. Thisis illustrated in FIG. 1, which shows the pH of various cleaningcompositions of the invention. The lines designated 100:1, 200:1 and500:1 refer to compositions prepared from the indicated volume parts ofwater:indicated volume parts of 49 wt % HF. Thus, 100:1 refers to acomposition prepared from 100 volume parts water and 1 volume part 49 wt% HF. The value “TMAH %” shown on the x-axis indicates the weightpercent of TMAH added to a particular composition, while the y-axisindicates the corresponding pH of the composition. The behavior shown inFIG. 1 is based on the published equilibrium constants for HF and TMAHin water.

As shown in FIG. 1, the pH of an aqueous HF composition is essentiallyconstant, up to a point, as TMAH is added to the composition. However,depending on the initial concentration of the aqueous HF, at some pointthe pH rapidly changes from acidic, and specifically from about 1 toabout 3, to alkaline, and specifically from about 11 to about 13. Acomposition that has a greater concentration of HF requires more TMAH tobecome alkaline. Thus, a composition prepared from 100 volume partswater and 1 volume part of 49 wt % aqueous HF (see solid line in FIG. 1)will maintain an acidic pH of about 2-3, until about 2.2 wt % TMAH hasbeen added (as a 25 wt % aqueous solution). However, when 500 volumeparts water and 1 volume part of 49 wt % aqueous HF are combined (seedashed line in FIG. 1) only about 0.4 wt % TMAH need be added to changethe solution from acidic to basic.

Preferred compositions of the invention are acidic, and more preferablyhave a pH of about 1-5. However, alkaline compositions, and specificallycompositions having a pH of about 9 to about 13, preferably about 11,may also be used in the invention and thus are also desirable.

The cleaning composition of the invention may be prepared from solvent(where water is a preferred solvent), HF and TAAH. While theseingredients may be combined in any order, a preferred order is thefollowing. HF, preferably aqueous HF, is added gradually to the solvent(preferably water) to form dilute HF. Then aqueous TAAH is addedgradually to the dilute HF. Each of the additions is preferablyaccompanied with stirring, or some other mechanized mixing process.

In a preferred process for preparing the cleaning composition, 0.01 to100 volume parts of 0.1 to 50 wt % aqueous HF are added to 100 volumeparts of water to form dilute HF, and then 0.01 to 100 volume parts of0.1 to 25 wt % aqueous TAAH are added to the dilute HF. More preferably,0.1 to 10 volume parts of 10 to 50 wt % aqueous HF are added to 100volume parts of water to form dilute HF, and then 0.1 to 10 volume partsof 5 to 25 wt % aqueous TAAH are added to the dilute HF. It should beunderstood that “volume parts” refer to volumes that are relative to theother volumes used in the process. Thus, a process wherein 100 volumeparts water are combined with 100 volume parts 49 wt % HF describes allprocesses wherein equal volumes of water and 49 wt % are combined.

When preparing a cleaning composition from TAAF, the TAAF is combinedwith a solvent to achieve a TAAF concentration of 0.01 to 10 weightpercent, preferably 0.05 to 5 weight percent, and more preferably 0.1 to2 weight percent based on the total weight of the cleaning composition.The TAAF-containing composition is preferably aqueous, in that there isat least some water present in the cleaning composition. The compositionmay have a neutral, acidic or alkaline pH, however preferably the pH isacid or alkaline, and more preferably the pH is acidic. A pH of about1-5 is preferred with a pH of about 3.5 being more preferred. Thecleaning composition may be made acidic through e.g., the addition ofhydrofluoric acid to the TAAF/solvent composition, or may be madealkaline through, e.g., the addition of TAAH to the TAAF/solventcomposition. An exemplary cleaning composition may be prepared by mixingtogether 425 g of tetramethylammonium fluoride, 70 mL of 25% aqueoushydrofluoric acid and 50 liters of water. A cleaning composition mayalso be prepared from TAAF, TAAH, HF and, optionally, water.

When a composition containing surfactant and/or organic solvent is to beprepared, the surfactant and/or organic solvent may be added to thecleaning composition at any time.

Having fully described the cleaning composition of the invention and itspreparation, its use in semiconductor fabrication will be describednext. According to the invention, the cleaning composition is employedto remove residue that results from a planarization process. As usedherein, the term planarization includes within its meaning the typicalmeaning given to “planarization” in the art. Thus, planarization isintended to include processes sometimes referred to in the art asflattening, leveling, smoothing, global planarization, localplanarization and the like, where such terms convey the idea that theprocess provides for a planar surface. In addition, planarization asused herein includes polishing processes. Sometimes “polishing” and“planarization” processes are distinguished from each other in the art(see, e.g., U.S. Pat. No. 5,441,094), however quite commonly these termsare used interchangeably. Nevertheless, for purposes of describing thepresent invention, planarization includes those processes that aresometimes referred to in the art as polishing, including blanketpolishing, as long as a residue results. Thus, planarization as usedherein specifically includes mechanical polishing (MP) andchemical-mechanical polishing (CMP), where the MP or CMP is used forproviding a planar surface or for any ultimate purpose, such as simplyremoving a layer from a semiconductor device. In fact CMP is a preferredplanarization process according to the present invention.

Planarization as used herein includes, but is not limited to, theplanarization (or polishing, leveling etc.) processes which aredescribed and/or discussed in the following U.S. Patents, which arefully incorporated herein by reference for all purposes: U.S. Pat. Nos.5,486,265; 5,461,007; 5,459,096; 5,457,070; 5,451,551; 5,449,314;5,445,996; 5,441,094; 5,434,107; 5,433,650; 5,422,289; 5,395,801;5,385,866; 5,362,669; 5,356,513; 5,354,490; 5,340,370; 5,332,467;5,318,663; 5,169,491; 5,084,419 and 5,084,071. CMP is a preferredplanarization process, and apparatus to perform CMP are described in thefollowing U.S. Patents, which are fully incorporated herein by referencefor all purposes: U.S. Pat. Nos. 5,486,129; 5,435,772; 5,142,828;5,036,015 and 3,841,031.

In addition, planarization as used herein includes those dry etchingprocesses that are directed to providing a planar surface. See, e.g.,the discussion in U.S. Pat. No. 5,407,526 to Danielson, et al., whereina dielectric layer having an uneven surface is coated with a layer ofmetal, to thereby fill in the indentations of the dielectric layer.Thereafter, the metal layer is evenly removed by dry etching until thedielectric layer is exposed, and a planar surface composed of dielectricand regions of metal, results. Danielson et al., which is fullyincorporated herein by reference for all purposes, states that this dryetching process typically leaves etch residue and metal particles on theplanarized surface.

Another method which is used to produce a planar semiconductor wafersurface is to initially spin coat the wafer with photoresist. The spincoating of photoresist on the wafer surface fills the low points andproduces a planar upper surface from which to start. Next, a dry etchwhich removes photoresist and oxide at a rate sufficiently close to 1:1,removes the photoresist and the high points of the wafer, therebyproducing a substantially planarized oxide layer on the wafer surface.This process may also generate residue on the planarized oxide surface,after the dry etching process is complete.

It is very typically the case that planarization will leave some residueon the planarized surface. The prior art contains many references tosuch residue. See, e.g., U.S. Pat. No. 5,434,107 to Paranjpe, whichrefers to post-process wafer clean up after chemical mechanicalpolishing, and to U.S. Pat. No. 5,407,526 to Danielson et al., asdiscussed above. Such residue is variously referred to in the art asplanarization residue, etch residue, post-planarization residue orsimply residue. Such residue may also be called contaminant, polishingresidue, film residue, debris, detritus and the like. The presentinvention is directed to semiconductor fabrication wherein aplanarization process achieves both a planar surface and residue on thatsurface, regardless of the specific name given in the art to thatresidue.

Because planarization residue has been frequently referred to in theprior art, it is believed that one of ordinary skill in the art readilyrecognizes planarization residue as that term is used herein. Ingeneral, the precise composition of the planarization residue depends ona number of factors, including the details of the planarization processand the composition of the surface being subjected to planarization. Itis generally true, however, that the planarization residue is notchemically bonded to the surface of the semiconductor device, where“chemically bonded” refers to the chemical bonds that bind together thesurface atoms of the semiconductor device. The chemical bonds that bindthese surface atoms are generally covalent bonds, and thus theplanarization residue being contemplated by the invention is notcovalently bound to the semiconductor device. Instead, the planarizationresidue sits on top of a semiconductor device, and may held in place byfriction, ionic bonds, van der Waals forces and other non-covalentbonds.

A single planarization residue may consist of a variety of chemicalspecies which are formed during a planarization process. For example,where planarization physically abrades the surface of the semiconductordevice, this may give rise to particles of residue that have the samechemical composition as the device surface. In some instances,planarization may achieve physical abrasion along with chemicalreactions at the device surface, where the chemical reactions facilitateremoval of surface atoms. In this instance, the residue may containparticles that have the same composition as the surface, as well asparticles that have modified compositions.

As another example, the wafer surface may be photoresist, in which casethe planarization residue may be pieces of either cured or uncuredphotoresist. As yet another example, the wafer surface may bespin-on-glass (SOG), in which case the planarization residue may beparticles of SOG.

In addition, the planarization residue may consist, in part or in whole,of abrasives that were used in the planarization process. This isparticularly likely to be true where the planarization process ischemical-mechanical polishing (CMP). CMP typically employs a particulateabrasive, along with a solvent, a surface-reactive chemical (e.g., anoxidizer, reducer and/or etchant) and a polishing pad. The particulateabrasive may be formed from any of a large number of materials,including aluminum oxide (alumina), boron carbide, boron suboxide (see,e.g., U.S. Pat. No. 5,456,735 to Ellison-Hayashi), cerium oxide (ceria);silicon carbide, and probably most commonly, silicon dioxide (silica,colloidal silica), to name a few. Thus, the planarization residue maycontain one or more of these abrasives.

One aspect of the present invention is a method of removing such residuefrom a surface after a planarization process. The problem of removingplanarization residue after a planarization process has been addressedin the semiconductor fabrication art. See, e.g., U.S. Pat. No. 5,478,436to Winebarger et al. and U.S. Pat. No. 5,389,194 to Rostoker et al.,where both of these patents are directed to chemical compositionsreportedly useful in removing planarization residue from a semiconductordevice. Both of these patents are fully incorporated herein by referencefor all purposes. Methodology for using the inventive compositions toremove planarization residue will be discussed next.

To allow the cleaning composition of the invention to removeplanarization residue from a planarized semiconductor device, thecomposition must be contacted with the residue. Any method known in theart for using a liquid composition to assist in, or achieve, removal ofplanarization residue may also be practiced with the inventivecomposition. For example, the residue-removal methods described ineither of U.S. Pat. Nos. 5,478,436 and 5,389,194, already incorporatedherein by reference, may be employed using the aqueous HF/TAAH or TAAFcomposition of the invention. However, a few specific methods accordingto the invention that can be used to remove planarization residue willnow be described.

A semiconductor device having planarization residue may be placed into abath of the cleaning composition (where the “cleaning composition”includes a liquid composition comprising TAAF and/or the result ofcombining solvent, HF and TAAH, both as described herein), whereuponplanarization residue will become suspended, dispersed and/or dissolvedin the cleaning composition and the device surface will becomerelatively free of the residue. It is also possible to place theresidue-containing device into a bath comprising one or two componentsof the cleaning composition (e.g., water and TAAH), and then meter-inthe remaining one or two components (e.g., HF). Elevated temperature maybe employed to hasten residue removal, although elevated temperature mayconcomitantly and undesirably hasten removal of atoms that form theplanarized surface, as discussed later herein.

It is preferred that some mechanical action take place while thecleaning composition contacts the residue-containing device surface, inorder to facilitate removal of the residue from the surface. Forexample, the bath of cleaning composition may be a recirculating bath,in order that a current of cleaning composition regularly passes overthe residue-containing surface. Alternatively, or in addition, the bathmay be an ultrasonic or megasonic bath (depending on the frequency ofvibration). As another example, the cleaning composition may be sprayedonto the device surface, where the spray pressure assists in removingresidue from the device surface. As a further example, scrubbing action,as provided, for example, by a brush, in combination with the cleaningcomposition, may be employed. Devices (known as scrubbers) intended forthe removal of planarization residue, which provide scrubbing actionthrough brushes (typically brushes made from PVA), are commerciallyavailable and known to one of ordinary skill in the art.

The preferred method of contacting the residue-containing surface withthe cleaning composition may depend, in part, on the nature of theresidue-containing surface and the details of the planarization processthat formed the residue. For example, where chemical-mechanicalpolishing has been used with an alumina slurry to remove tungsten metalfrom a device surface, the device may be placed into a circulating ornon-circulating ultrasonic or megasonic bath of water and TMAH, and thena dilute solution of HF is gradually added to the bath. After some time,the device is removed from this bath, rinsed with water, and then placedinto a scrubber with TMAH and water at an alkaline pH, for examplegreater than about 9.5. Thereafter the device is again rinsed with waterand is essentially free of planarization residue. The device may bedried (i.e., freed of solvent) by Marangoni drying, as known in the art.As illustrated by this procedure, contacting a residue-containing devicewith the cleaning composition of the present invention may be one ofseveral separate steps in a process to remove planarization residue froma device surface.

As illustrated by the above example, it is not necessary to pre-form thecleaning composition before contacting the composition with theresidue-containing surface. The surface may first be contacted with oneor two of the components used to prepare the cleaning composition, andthen the remaining components may be added, either alone or separately,either in one shot or metered in. Because various components of thecomposition may be metered into a batch solution at various times andrates, it is difficult to precisely define the concentration of each ofthe components that are contacted with the surface. However, theinventive method includes the method wherein the various components ofthe cleaning composition are sequentially added to an environment thatalso contains the residue-containing surface.

The inventive composition and methods may also be employed in instanceswhere the planarization residue results from chemical mechanicalpolishing of TEOS-derived ILD (interlayer dielectric) surface materialor doped silica glass. In these cases, the planarized device may beplaced in a bath of aqueous HF/TMAH, followed by a megasonic bath ofaqueous TMAH, followed by being scrubbed in an aqueous bath, optionallywith one or more of HF and TMAH. Commercial scrubbing equipment commonlyhas the ability to spin dry a scrubbed wafer, and thus the wafer may bedried in this manner within the scope of the present invention.

It should be understood that while certain specific cleaning protocolshave been detailed above in connection with certain specifiedplanarization processes and surface compositions, the specific cleaningprotocols may be used with other planarization processes and surfacecompositions, and the residue resulting from the specified planarizationprocesses and surface compositions may be removed by alternativecleaning procedures. The above are merely illustrative of the invention.For example, a semiconductor wafer having planarization residue thereonmay be placed into a bath formed from water and TAAF. Thereafter, ifnecessary for complete cleaning, HF and/or TAAH may be added to theaqueous TAAF bath.

As suggested by the above examples, the cleaning composition and methodsof the invention may desirably be tailored to the identity of the devicesurface. This is because, for example, while the cleaning compositionand methods are very well-suited to removing residue from a devicesurface, the same composition and methods may also result in someremoval of the atoms that form the surface of the device. Thus, while ina preferred embodiment, the inventive method removes only residue andnot surface atoms, the inventive method may remove surface atoms inaddition to removing residue. Thus, the inventive method should bepracticed with a view to its effect on the planarized surface of thesemiconductor device, as discussed further below.

According to a preferred embodiment of the invention, chemicalmechanical polishing is the planarization process that provides a planarsurface with residue thereon. The present invention is particularlysuited to substantially removing all residue from a planarized surfacethat has been subjected to CMP, and is especially well-suited toremoving residue resulting from a CMP process that employs silica as anabrasive and acts on doped silica substrate. That the aq. HF/TAAHcomposition of the invention is particularly well-suited for such CMPprocesses can be seen from the following described experiment.

The etch rates of an inventive cleaning composition (aqueous HF/TMAH anda TMAH-free composition (aqueous HF) with both a doped and undopedsilica substrate, were determined. To determine etch rate, a laminatehaving a top layer formed from a known thickness of silica was placedinto a bath of each of the aforementioned compositions. After a measuredtime, the laminate was removed from the bath, and the thickness of thetop layer was measured. The decrease in thickness of the top layer,divided by the time the layer was in the bath, provides the etch ratefor the particular liquid composition and substrate composition.

TABLE 1 compares aqueous HF and aqueous HF/TMAH for their abilities toetch BPSG (a boron and phosphorous doped silica glass) and undopedsilica (such as produced by the decomposition of tetraethylorthosilicate(TEOS)).

TABLE 1 Etch rates for aq. HF and aq. HF/TMAH with doped and undopedsilica Etch Rate (Å/min) Identity of substrate etchant is etchant isbeing etched aq. HF aq. HF/TMAH Undoped Silica 25 25 Doped Silica (BPSG)250-400 55

TABLE 1 shows that the etch rate for undoped silica is about 25 Å/minusing either aqueous HF or aqueous HF/TMAH. However, when BPSG is beingetched, the etch rate using aqueous HF is about 250-400 Å/min, while itis only about 55 Å/min using aqueous HF/TMAH.

The inventive composition and methods are thus shown to be particularlywell-suited for removing CMP-derived residue from a surface formed ofdoped silica This is particularly the case when silicon dioxide is usedas an abrasive in a CMP process, and the doped silica contains boronand/or phosphorus dopants, e.g., PSG or BPSG. Including TMAH in anaqueous HF cleaning composition has unexpectedly been found todramatically retard the extent to which the composition dissolves(etches) doped silica, while having essentially no effect on the rate atwhich undoped silica is dissolved. In fact, the presence of TMAH mayreduce by about five-fold the extent to which aqueous HF dissolves dopedsilica. Thus, the inventive composition is particularly useful inremoving silica residue from a planarized BPSG surface.

The relative amounts of water, HF, TAAH and/or TAAF used to prepare thecleaning composition will influence the selectivity of the compositionin removing residue versus removing atoms from the substrate surfaceitself. Routine experimentation may be needed in order to find acomposition that provides optimal cleaning ability with minimaldegradation of the semiconductor surface.

BPSG surfaces, and planarization of the same, are common features ofsemiconductor fabrication. For example, in the preparation ofpolysilicon plugs and containers in semiconductor devices, a layer ofBPSG may be deposited over the plug or container. Thereafter, the BPSGlayer may be planarized using a silica-containing slurry in a CMPprocess. It is desirable that all of the planarization residue, whichtypically includes particulate silica, be removed after the CMP process.However, it is undesirable that the BPSG layer be removed to the extentof exposing the underlying plug or container. Using a cleaningcomposition containing only water and hydrofluoric acid, the rate ofBPSG removal is such that by the time the planarization residue iscompletely removed, sufficient BPSG has also been removed such that theunderlying plug or container may be exposed. However, when TMAH (orother TAAH) is added to the aqueous HF cleaning solution, the rate ofBPSG removal is sufficiently retarded (without effecting the rate ofsilica removal) that a layer of BPSG remains over the plug or containerafter complete removal of the planarization residue.

The following U.S. patents, which are fully incorporated herein byreference for all purposes and are exemplary only, provide details ofsemiconductor device manufacture wherein the semiconductor devicecontains plug and/or container features: U.S. Pat. Nos. 5,407,526;5,340,763; and 5,354,705.

Having described the inventive cleaning composition, its manner ofpreparation and its use in removing residue formed during aplanarization process, a preferred method according to the invention forsemiconductor fabrication will be described in connection with FIG. 2.Thus, a device 10 a having a substrate layer 12 and an overlying layer14 is provided. The layer 14 has a surface 16 of uneven topography. In afirst step, denoted (1) in FIG. 2, a planarization process (not shown)is used to remove material extending above the lowest point of thesurface 16. As a consequence, the device 10 b is formed, having asubstrate layer 12 and an overlying layer 14 formed in part of a planarsurface 18. In addition, sitting on top of the planar surface 18 is aresidue 20 that is a consequence of the planarization process. “X” and“O” in FIG. 2 merely indicates that the residue 20 may comprise morethan one chemical species.

The planarization residue 20 is removed in a second step, denoted (2) inFIG. 2. In step (2), the device 10 b is placed into a bath 22 preparedby combining water, HF and TMAH (or other TAAH). As shown in FIG. 2, theresidue 20 starts to dissolve and/or become suspended in the bath 22,resulting in a partially clean device 10 c. After some time has passed,denoted by step (3) in FIG. 2, substantially all of the planarizationresidue is suspended and/or dissolved in the bath 22, and the resultingdevice 10 d has a surface 18 which is planar and essentially free ofresidue. In step (4), the device 10 d is removed from the bath and driedto provide device 10 e, which is ready to be modified by additionalsteps in semiconductor wafer fabrication.

Although the present invention has been described hereinabove primarilywith reference to the removal of planarization residue resulting fromchemical mechanical polishing of a semiconductor wafer, it should beunderstood that the invention can be applied to the removal of residue,debris, detritus, etc. (collectively “planarization residue”) thatresults from other processes that may be performed during semiconductorfabrication. In this regard, it should be readily apparent to thoseskilled in the art that the present invention can be used to cleanresidue resulting from any planarization process that produces residueas a byproduct of planarization.

While the invention has been described in terms of specific embodiments,it is evident in view of the foregoing description that numerousalternatives, modifications and variations will be apparent to thoseskilled in the art. Thus, the invention is intended to encompass allsuch alternatives, modifications and variations which fall within thescope and spirit of the invention and the appended claims.

We claim:
 1. A composition for cleaning a semiconductor device whereinthe composition has an acidic pH and is comprised of a combination ofsolvent, hydrofluoric acid (HF) and tetraalkyylammonium hydroxide(TAAH), wherein TAAH has the formula (R)₄NOH and each occurrence of R isindependently selected from a C₁₋₂₂alkyl group, wherein the compositionresults from the combination of water, hydrofluoric acid (HF) andtetraalkylammonium hydroxide (TAAH), provided that a surfactant ispresent in the cleaning composition at a concentration of about 0.001 wt% to about 10 wt % based on the total weight of the cleaning solution.2. The composition of claim 1 wherein the cleaning composition resultsfrom the combination of water, 49 wt % aqueous HF and 25 wt % aqueousTAAH in a water:HF:TAAH volume parts ratio of 100:0.01-100:0.01-100. 3.The composition of claim 2 wherein the volume parts ratio is100:0.1-10:0.01-10.
 4. The composition of claim 2 wherein the volumeparts ratio is 100:0.5-2:0.5-5.
 5. The composition of claim 1 whereinTAAH is tetramethylammonium hydroxide.
 6. The composition of claim 2wherein the solvent is selected from water, methanol, ethanol,n-propanol, iso-propanol, n-butanol, sec-butanol, iso-butanol,t-butanol, ethylene glycol and propylene glycol.
 7. The composition ofclaim 2 wherein the acidic pH is about 1 to about
 5. 8. The compositionof claim 2 wherein R is independently C₁₋₄alkyl at each occurrence. 9.The composition of claim 2 wherein organic solvent is present in thecleaning composition at a concentration of about 0.01 wt % to 95 wt %based on the total weight of the cleaning composition.
 10. A compositionfor cleaning a semiconductor device comprising, an organic solvent at aconcentration of about 0.01 wt % to 95 wt % based on the total weight ofthe cleaning composition, hydrofluoric acid (HF) and tetraalkylammoniumhydroxide (TAAH), wherein the cleaning composition comprises thereaction product of hydrofluoric acid (HF) and tetraalkylammoniumhydroxide (TAAH), wherein TAAH has the formula (R)₄NOH wherein TAAH hasthe formula (R)₄NOH and each occurrence of R is independently selectedfrom a C₁₋₂₂alkyl group.
 11. The composition of claim 10 wherein thecleaning composition comprises the reaction product of 49 wt % aqueousHF and 25 wt % aqueous TAAH in a water:HF:TAAH volume parts ratio of100:0.01-100:0.01-100.
 12. The composition of claim 11 wherein thevolume parts ratio is 100:0.1-10:0.01-10.
 13. The composition of claim11 wherein the volume parts ratio is 100:0.5-2:0.5-5.
 14. Thecomposition of claim 10 wherein TAAH is tetramethylammonium hydroxide.15. The composition of claim 10 wherein the organic solvent is selectedfrom methanol, ethanol, n-propanol, iso-propanol, n-butanol,sec-butanol, iso-butanol, t-butanol, ethylene glycol and propyleneglycol.
 16. The composition of claim 10 wherein the cleaning compositionhas an alkaline pH.
 17. The composition of claim 16 wherein the alkalinepH is about 9 to about
 13. 18. The composition of claim 10 wherein thecleaning composition has an acidic pH.
 19. The composition of claim 18wherein the acidic pH is about 1 to about
 5. 20. The composition ofclaim 10 wherein R is independently C₁₋₄alkyl at each occurrence. 21.The composition of claim 10 wherein surfactant is present in thecleaning composition at a concentration of about 0.001 wt % to about 10wt % based on the total weight of the cleaning composition.
 22. Aprocess for making a cleaning composition for treating a semiconductorworkpiece comprising, combining water, hydrofluoric acid (HF) andtetraalkylammonium hydroxide (TAAH), wherein TAAH has the formula(R)₄NOH and each occurrence of R is independently selected from aC₁₋₂₂alkyl group, and adjusting the composition to an acidic pH.
 23. Theprocess of claim 22 wherein the cleaning composition results fromcombining water, 49 wt % aqueous HF and 25 wt % aqueous TAAH in awater:HF:TAAH volume parts ratio of 100:0.01-100:0.01-100.
 24. Theprocess of claim 23 wherein the volume parts ratio is100:0.1-10:0.01-10.
 25. The process of claim 23 wherein the volume partsratio is 100:0.5-2:0.5-5.
 26. The process of claim 22 wherein TAAH istetramethylammonium hydroxide.
 27. The process of claim 22 furtherincluding combing an organic solvent selected from water, methanol,ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, iso-butanol,t-butanol, ethylene glycol and propylene glycol.
 28. The process ofclaim 22 wherein the acidic pH is about 1 to about
 5. 29. The process ofclaim 22 wherein R is independently C₁₋₄alkyl at each occurrence. 30.The process of claim 22 further including combining a surfactant at aconcentration of about 0.001 wt % to about 10 wt % based on the totalweight of the cleaning composition.
 31. The process of claim 22 furtherincluding combining an organic solvent at a concentration of about 0.01wt % to 95 wt % based on the total weight of the cleaning composition.32. A process for making a cleaning composition for a semiconductordevice comprising, combining an organic solvent at a concentration ofabout 0.01 wt % to 95 wt % based on the total weight of the cleaningcomposition, with hydrofluoric acid (HF) and tetraalkylammoniumhydroxide (TAAH), wherein the components include the combination ofwater, 49 wt % aqueous HF and 25 wt % aqueous TAAH in a water:HF:TAAHvolume parts ratio of 100:0.01-100:0.01-100, wherein TAAH has theformula (R)₄NOH and each occurrence of R is independently selected froma C₁₋₂₂alkyl group.
 33. The process of claim 32 wherein the volume partsratio is 100:0.1-10:0.01-10.
 34. The process of claim 32 wherein thevolume parts ratio is 100:0.5-2:0.5-5.
 35. The process of claim 32wherein TAAH is tetramethylammonium hydroxide.
 36. The process of claim32 wherein the organic solvent is selected from methanol, ethanol,n-propanol, iso-propanol, n-butanol, sec-butanol, iso-butanol,t-butanol, ethylene glycol and propylene glycol.
 37. The process ofclaim 32 wherein the components are combined to form a compositionhaving an alkaline pH.
 38. The process of claim 37 wherein the alkalinepH is about 9 to about
 13. 39. The process of claim 32 wherein thecomponents are combined to form a composition having an acidic pH. 40.The process of claim 32 wherein the acidic pH is about 1 to about
 5. 41.The process of claim 32 wherein R is independently C₁₋₄alkyl at eachoccurrence.
 42. The process of claim 32 further including combining asurfactant to form a composition comprising about 0.001 wt % to about 10wt % surfactant based on the total weight of the cleaning composition.43. The process of claim 32 wherein the organic solvent is combined toform composition having an organic solvent concentration of about 0.01wt % to 95 wt % based on the total weight of the cleaning composition.44. A composition for cleaning a semiconductor device wherein thecomposition has an acidic pH and is comprised of a combination ofsolvent, hydrofluoric acid (HF) and tetraalkylammonium hydroxide (TAAH),wherein TAAH has the formula (R)₄NOH and each occurrence of R isindependently selected from a C₁₋₂₂alkyl group, wherein the cleaningcomposition results from the combination of water, 49 wt % aqueous HFand 25 wt % aqueous TAAH in a water:HF:TAAH volume parts ratio of100:0.01-100:0.01-100, provided that a surfactant is present in thecleaning composition at a concentration of about 0.001 wt % to about 10wt % based on the total weight of the cleaning solution.
 45. Thecomposition of claim 44 wherein the volume parts ratio is100:0.1-10:0.01-10.
 46. The composition of claim 44 wherein the volumeparts ratio is 100:05-2:0.5-5.
 47. The composition of claim 44 whereinTAAH is tetramethylammonium hydroxide.
 48. The composition of claim 44wherein the solvent is selected from water, methanol, ethanol,n-propanol, iso-propanol, n-butanol, see-butanol, iso-butanol,t-butanol, ethylene glycol and propylene glycol.
 49. The composition ofclaim 44 wherein the acidic pH is about 1 to about
 5. 50. Thecomposition of claim 44 wherein R is independently C₁₋₄alkyl at eachoccurrence.
 51. The composition of claim 44 wherein organic solvent ispresent in the cleaning composition at a concentration of about 0.01 wt% to 95 wt % based on the total weight of the cleaning composition. 52.A process for making a cleaning composition for a semiconductor devicecomprising, combining an organic solvent at a concentration of about0.01 wt % to 95 wt % based on the total weight of the cleaningcomposition, with hydrofluoric acid (HF) and tetraalkylammoniumhydroxide (TAAH), wherein TAAH is tetramethylammonium hydroxide andwherein TAAH has the formula (R)₄NOH and each occurrence of R isindependently selected from a C₁₋₂₂alkyl group.
 53. The process of claim52 wherein the volume parts ratio is 100.0.1-10:0.01-10.
 54. The processof claim 52 wherein the volume parts ratio is 100:0.5-2:0.5-5.
 55. Theprocess of claim 52 wherein the organic solvent is selected frommethanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol,iso-butanol, t-butanol, ethylene glycol and propylene glycol.
 56. Theprocess of claim 52 wherein the components are combined to form acomposition having an alkaline pH.
 57. The process of claim 52 whereinthe alkaline pH is about 9 to about
 13. 58. The process of claim 52wherein the components are combined to form a composition having anacidic pH.
 59. The process of claim 52 wherein the acidic pH is about 1to about
 5. 60. The process of claim 52 wherein R is independentlyC₁₋₄alkyl at each occurrence.
 61. The process of claim 52 furtherincluding combining a surfactant to form a composition comprising about0.001 wt % to about 10 wt % surfactant based on the total weight of thecleaning composition.